1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for establishing a device-to-device (D2D) connection in a wireless communication system.
2. Related Art
In next generation multimedia mobile communication systems, which have been actively studied in recent years, there is a demand for a system capable of processing and transmitting a variety of information (e.g., video and radio data) in addition to the early-stage voice service. Further, a 3rd generation wireless communication system is followed by a 4th generation wireless communication which is currently being developed aiming at supporting a high-speed data service of 1 gigabits per second (Gbps) in downlink and 500 megabits per second (Mbps) in uplink. The wireless communication system is designed for the purpose of providing reliable communication to a plurality of users irrespective of their locations and mobility. However, a wireless channel has an abnormal characteristic such as a fading phenomenon caused by a path loss, noise, and multipath, an inter-symbol interference (ISI), a Doppler effect caused by mobility of a user equipment, etc. Therefore, various techniques have been developed to overcome the abnormal characteristic of the wireless channel and to increase reliability of wireless communication.
Meanwhile, with the advent of a ubiquitous environment, there is a rapid increase in a demand for receiving a seamless service anytime anywhere by using equipments. In order to satisfy such a demand, a device-to-device (D2D) connection technique may be introduced in a wireless communication system. The D2D connection technique refers to a technique for transmitting and receiving data not via a base station (BS) since devices such as a user equipment (UE) or the like are connected to each other. That is, one device can communicate with another device via the BS, and can directly communicate with another device not via the BS. By using the D2D connection technique, such an effect as low power consumption, throughput enhancement, etc., can be obtained.
Various scenarios may exist to establish the D2D connection. There may be a D2D connection scenario on the basis of whether the D2D connection establishment is initiated by the BS or each device. In addition, there may be a D2D connection scenario on the basis of whether information regarding another device neighboring to a specific device is known to the BS and/or the specific device.
There is a need for a method of effectively establishing a D2D connection when a network does not know information on neighbor devices of a specific device and only the specific device knows the information on the neighbor devices of the specific device.